Membrane valves, which are particularly advantageous in biotechnology, the food industry and the pharmaceutical industry where aseptic conditions must be maintained, are also known as aseptic valves since they can maintain aseptic conditions in the fluid compartment of the valve which is separated from the actuator compartment by a membrane.
In many conventional membrane valves, the membrane is composed of natural rubber or a synthetic elastomer. With such materials, in use, relatively soon small cracks can arise in the membrane which can be populated by bacteria. Such valves, while they may continue to retain their sealing function, nevertheless become unsuitable for aseptic systems.
Aseptic valves of the bellows-valve type have also been proposed, the valve bellows being composed of stainless steel. Between the ribs or corrugations of the bellows, however, contaminants can readily accumulate and the useful life of the bellows is therefore quite limited. When efforts are made to coat the metal bellows with synthetic resin materials, such as polytetrafluoroethylene, however, the same problems arise as have been described in conjunction with elastomer membranes.
U.S. Pat. Nos. 4,671,490 and 4,750,709 describe membrane valves of the type first mentioned above and in which a welding of the membranes is affected to hold the layers of the membrane together. To anchor the membrane to the membrane ring and sealing member, however, clamping systems are used and/or clamping systems are provided to relieve the weld locations from stresses arising with the actuation of the valves. As a consequence, associated with the membranes are steps, discontinuities and crevices, especially at the clamping locations, at which bacteria can accumulate.